A mass spectrometer is an analytical instrument that separates and detects ions according to their mass-to-charge ratio. Mass spectrometers can be differentiated based on whether trapping or storage of ions is required to enable mass separation and analysis. Non-trapping mass spectrometers do not trap or store ions, and ion densities do not accumulate or build up inside the device prior to mass separation and analysis. Examples in this class are quadrupole mass filters and magnetic sector mass spectrometers in which a high power dynamic electric field or a high power magnetic field, respectively, are used to selectively stabilize the trajectories of ion beams of a single mass-to-charge (m/q) ratio. Trapping spectrometers can be subdivided into two subcategories: dynamic traps, such as, for example, quadrupole ion traps (QIT) and static traps, such as the more recently developed electrostatic confinement traps.
Electrostatic confinement traps include the ion trap disclosed by Ermakov et al. in their PCT/US2007/023834 application that confines ions of different mass-to-charge ratios and kinetic energies within an anharmonic potential well. The ion trap is also provided with a small amplitude AC drive that excites confined ions. The amplitudes of oscillation of the confined ions are increased as their energies increase, due to a coupling between the AC drive frequency and the mass-dependent natural oscillation frequencies of the ions, until the oscillation amplitudes of the ions exceed the physical dimensions of the trap and the mass-selected ions are detected, or the ions fragment or undergo any other physical or chemical transformation.
The electrostatic ion trap disclosed by Ermakov et al. was improved by Brucker et al. in their PCT/US2010/033750 application. The use of anharmonic potentials to confine ions in an oscillatory motion enables much less complex fabrication requirements and much less stringent machining tolerances than are required in harmonic potential electrostatic traps, where strict linear fields are a requirement, because the performance of the trap is not dependent upon a strict or unique functional form for the anharmonic potential. Therefore, mass spectrometry or ion-beam sourcing performance is less sensitive to unit-to-unit variations, allowing more relaxed manufacturing requirements for an anharmonic resonant ion trap mass spectrometer (ART MS) compared to most other mass spectrometers.